A steered and driven axle-end assembly normally has a knuckle formed of inside and outside knuckle halves pivotal relative to each other about an upright pivot axis, the inside knuckle half being mounted rigidly on the frame of the vehicle. An axle extends into the inside knuckle half and is connected there to the inner side of a universal joint whose outer side is connected to a wheel support that is rotatable about a horizontal wheel axis by means of roller bearings that support it on the outer knuckle half. Thus it is possible for the outside knuckle half to pivot with the wheel carried on the wheel support relative to the inside half while rotary force is still transmitted through the universal joint, which is normally of the constant-speed type, to the wheel.
In heavy-duty construction equipment it is desirable to provide the wheel brake inboard of the wheel on the axle. This is made possible by providing stepdown gearing between the outside joint half and the rotatable wheel support. The axle therefore rotates at a considerably greater angular rate than the wheel so that brakes suitable for high speed and low torque can be employed, thereby saving considerable expense. This type of arrangement also has the advantage that the bearings and the like that support the axle or drive shaft can also be of the high-speed low-torque type which is considerably cheaper to manufacture and which has longer service life than the type adapted for low-speed high-torque use.
The main disadvantage of these systems, however, is that they are relatively bulky. The distance between the knuckle and the wheel is relatively great so that quite a bit of mechanism is exposed under the vehicle at each wheel. In construction equipment this disadvantage is very great in that this mechanism is exposed to damage from the rough terrain on which the vehicle rides.
Another considerable disadvantage of such an arrangement is that its axial length, measured along the horizontal wheel axis, is so great that the wheel can only be cramped through a relatively limited arc from one end to the other of its travel about the upright pivot axis defined by the knuckle. The turning radius for the vehicle is therefore relatively large, another disadvantage in construction equipment which must normally be as maneuverable as possible.